High Flying monorail

General Electric Aircraft Engine Services (GEAES) has invested more than $30m in a test facility at Nantgarw near Caerphilly in Wales for its GE90 engine. It comprises an engine preparation workshop, test cell and control building and has been built as an extension to the existing facilities at the site, where more than 1,000 people are employed.

The GE90 extension includes an extensive monorail system to handle the engines, which each weigh around 10t on their own, increasing to 25t when they are fitted to the mounting frame used during testing and overhaul.

Purchased from British Airways in 1991, Nantgarw is the largest of five GEAES engine servicing facilities located around the world and has the capacity to overhaul 550 units per year. As well as GE’s own products, it is able to handle engines manufactured by CFM International, Rolls Royce and Pratt & Whitney.

The GE90 is the latest addition to the GE engine range and is fitted to the Boeing 777 wide bodied twin engine passenger jets. It is the most powerful unit ever certified for airline use, with thrust levels ranging from 76,000lb to 100,000lb and a highest recorded figure of 105,400lb. Nantgarw currently handles all GE90 overhaul work, including reworking of the development engines used during test programmes.

The test cell at Nantgarw is the first commercial facility to permit testing of engines with thrusts up to 150,000lb. A major objective of the design was to reduce noise pollution, so the cell is constructed with a 2m air gap between its inner and outer walls, giving a total wall thickness of 3.2m. This is a similar design to the Rolls Royce facility at Derby in England, which has 2.5m walls with a 1.5m air gap, and is suitable for engines of up to 100,000lb thrust.

Nantgarw is equipped with an overhead engine handling system which comprises:

• 210m of monorail

• two monorail bridge cranes

• one monorail turntable

• one 35t carrier

• one 15t carrier

• two 5t carriers

• 20 mechanical interlocks.

The system was supplied by CTI Systems of Luxembourg and uses the company’s patented TARCA monorail. This has a high carbon steel bottom flange/running rail, combined with a mild steel web and top flange, and runs throughout the workshop and test cell.

The two monorail bridge cranes are underslung from two parallel runways fixed to the structural steelwork in the aisle of the workshop. These are used to move engine carriers between the test cell and the workstation spurs in the engine preparation area.

The turntable, located in the access way between the workshop and the test cell, is basically a monorail bridge crane underslung from a circular TARCA runway fixed to the structural steelwork. It is used to rotate engines mounted on the 35t carrier so that they can enter the workstations either ‘tail-first’ or ‘fan-first’.

To enable closure of the test cell’s 52t steel-and-concrete sound proofed doors, a swivel beam is incorporated in the cell entrance area. This is a short length of monorail underslung from a slewing ring attached to the structure of the building.

The 35t carrier is used to transport fully equipped engines from the workstations to the test cell and back again. It is fitted with two 25t hoists, to allow for the centre of gravity being offset. The carrier is controlled by a programmable logic controller connected to absolute encoders on each of the hoists to give height control, to an optical unit that communicates with the thrust stand in the test cell, and to an inductive transmitter to communicate with the bridges.

The 15t carrier is used to transport stripped down GE90 engines and smaller engines such as the Rolls Royce RB211, while the two 5t carriers are used to move smaller components during the engine strip down, overhaul and rebuild process.

Work sequence

Engines arrive either on a ground cart or by truck and are off-loaded to one of the workstations in the workshop, where an engine adaptor is fitted. This is a large precision-made metal frame that has the same fixings as the underside of an aircraft wing. Fuel, hydraulic, air and coolant connections are then made and when the engine is ready to be run up, the 35t carrier is brought to the workstation and its autograb lowered onto the engine adaptor. The engine and adaptor are fully raised and transported to the test cell, where they are fitted into the thrust stand. As the package enters the stand, 200mm of slack rope is paid off the hoists and the control system signals the thrust stand to pull the engine adaptor into place, thus engaging the plugs and sockets. When this operation is completed, the carrier releases the adaptor and is raised to the fully up position. It is then removed from the test cell and can be used for other duties while the engine is being run up and tested.

Remote control system

Operational requirements and the height of the building meant that pendant control was not an option, so a Cattron radio remote control system was chosen. Precise control and mutually exclusive operation are vital, so each of the four engine carriers has a dedicated controller. Each of these controllers operates its own carrier and either of the two bridges. To enable the bridges to operate from a single controller, the decoders work on multiple frequencies and addresses. They constantly scan the frequencies for a valid signal and once this is received, they lock onto a single controller and ignore the others until the operation is complete.

The main 35t carrier is equipped with a Cattron MP96 controller to give the highest level of security and make ‘Talkback’ status indication available to the operator. This feature also allows the operator to verify that the locking pins are in place before the engine is lifted from its static cradle. An uninterruptible power supply has also been built into the decoder to enable continuous operation whilst the decoder is held on an unpowered turntable. H